The present invention relates to a cylinder control system for multicylinder internal combustion engines, and more particularly to improvements to a cylinder control system for a multicylinder internal combustion engine having an exhaust gas purification device and a plurality of fuel injection valves for injecting fuel into the cylinders of the engine.
Generally, operation of an internal combustion engine under a high load results in high fuel efficiency. Thus a cylinder control system for multicylinder internal combustion engines is known, by which, while the engine load is low, certain cylinders are not supplied with fuel, and the supply to the remaining working cylinders is increased by a corresponding amount so as to operate the engine in the range of high efficiency of fuel combustion.
If such a cylinder control system is provided in a fuel injection type multicylinder gasoline engine, certain cylinders to which the fuel supply is interrupted while the engine load is light will take in fresh air and discharge it, as is, into the exhaust passage. Accordingly, if a catalyst device is provided in the exhaust gas system, the cold air now discharged will lower the temperature of the catalyst and therefore the efficiency of purifying the exhaust gas by the catalyst, or the efficiency of reducing NO.sub.x when the catalyst is a three-way catalyst.
In view of this, we have proposed a device in which the intake passages to some of the cylinders, for example three predetermined cylinders of a 6-cylinder engine, to which fuel supply will be interrupted during light engine load, are separated from the intake passages of the remaining cylinders which will work at all times irrespective of the magnitude of the load. In addition, a valve is provided in the intake passage of the cylinders to which the fuel supply will be interrupted which is operable to close the intake passage so unused air does not flow into the exhaust gas passage while only the certain cylinders are being operated. (see Japanese Utility Model registration application 159832/1977.) This device prevents lowering of the temperature of the catalyst and therefore maintains the standard of exhaust gas purification.
If the valve does not operate, and more particularly if it remains closed or only partially open for some reason when it should be fully opened by an instruction to operate all the cylinders when the engine load is high, the cylinders concerned will not be supplied with air or with only insubstantial amounts of air but will be supplied with a normal amount of fuel by injection. Thus, the fuel will not be properly combusted but will be discharged from the cylinders thereby lowering the efficiency of fuel combustion and worsening the discharge of exhaust gases.
Most of the fuel injected into the cylinders into which air is not being properly supplied, may flow into the exhaust passage under the effect of the pulsations caused by the difference between the timings of injection of fuel into these cylinders, and further can be carried into the catalyst by the exhaust gas from the working cylinders. If the fuel thus discharged should be burned in a post-treatment device such as a catalyst device (reactor), the device will be burnt and its lifetime will be shortened.